Skip navigationOf new weapons and nuclear genies

 

 

1. Who's got the bomb?

2. How nukes work

3. Bring forth the 4th generation

4. Never say "never"

5. An end to the search?

  On Nov. 1, 1952, Ivy-Mike thermonuclear test blew off the equivalent of 10.4 million tons of TNT, practically obliterating Eniwetok Atoll in the Marshall Islands, Pacific Ocean. This was the first test of a two-stage bomb. Image from Nevada Site Office, U.S. Department of Energy

 

 

 

 

The primary, a fission bomb, makes X-rays that flow through the radiation channel, energizing the hohlraum and compressing the fusion fuel, triggering fusion. Courtesy Carey Sublette, Enviroweb.

 

Opening Pandora's nuclear war chest
Read about the invention of the atomic bomb, and you'll immediately recognize the intense scientific curiosity driving the crew at Los Alamos (see "The Making ..." in the bibliography) during World War II. Today, the elite scientists and engineers at the three nuclear-weapons labs are a highly motivated, well-funded crew, with a serious bunch of "boy's toys."

white mushroom-shaped cloud in distance against blue sky As nuclear scientist Hans Bethe pointed out, if anyone can invent new nuclear weapons, it is these folks.

The quest for fourth-generation nuclear weapons -- based on new physical principles and new ways to compress fusion fuel -- goes back to the early years of the nuclear labs, says Christopher Paine of the Natural Resources Defense Council. "It's been a Holy Grail of the [nuclear weapons] labs, to find a clean, low-yield, very compact nuclear explosive device."

The frustration, he says, is almost equally old. "They've had classified projects since the '50s ... and have never gotten there."

The reason is simple. Initiating fusion, as Paine says, "Is extremely difficult to do. ... The only way we've done it is with X-rays from another nuclear explosion. It takes a nuclear explosion to drive a nuclear explosion, and they have been searching for decades" to replace the fission stage of a thermonuclear bomb.

Without success.

Diagram shows two-chambered nuclear device including high explosive, reflector, levitated plutonium pit, uranium shield, polystyrene filled radiation channel, weapon case,....

The common element in many of the speculative methods for 4-gen weapons is finding a "better" way to compress fusion fuel (light atoms like hydrogen and helium). As you read our list of how such a "pure fusion" weapon might be made, note how much of the research was done at U.S. weapons labs:

Metallic hydrogen
When hydrogen is squeezed by about 1 million atmospheres of pressure, theory says the electrons will start to flow easily, making a good conductor or even a superconductor. This "metallic hydrogen" will, again theoretically, store immense amounts of energy.

A 1977 report (see "Molecular and..." in the bibliography), said metallic hydrogen would have 35 times the explosive capacity of TNT and could be "useful in nuclear weapons."

In 1996, metallic hydrogen was apparently synthesized at Lawrence Livermore National Laboratory (LLNL) in California, home of the thermonuclear bomb. In 1998, LLNL experimenters shocked deuterium (a hydrogen isotope with one neutron) with a giant laser, producing a material with metal-like superconducting properties.

That's progress, but it's not clear that the stuff could replace the fission stage, to make a pure fusion weapon.

Laser-initiated (inertial confinement) fusion
The Mercedes of fourth-generation research project is the National Ignition Facility (check that nifty acronym: NIF), 192 giant lasers being built at Lawrence Livermore. The goal is to focus enormous amounts of electromagnetic energy on a tiny fuel pellet and "ignite" fusion. The outside of the pellet is supposed to vaporize and compress the fuel.

 high-tech chamber with half sphere shaped mass in center of room
Brief blasts of ultra-high-energy laser light are supposed to initiate fusion in this chamber at the National Ignition Facility at Lawrence Livermore National Lab. The 192 giant lasers of NIF are supposed to simulate conditions inside a nuclear explosion, but critics say it could help design fourth-generation nuclear weapons - if it works. Lawrence Livermore National Lab.

The Fusion Group at General Atomics Corp says the mission of the Inertial Confinement project is "to provide a thermonuclear capability in the laboratory for defense and ultimately civilian applications."

By simulating conditions inside a thermonuclear weapon, NIF is supposed to support research on the effects of aging on the U.S. nuclear arsenal. While the seven-acre, $3-billion laser itself would obviously not make a weapon -- it's a bit big and pricey for a bomb, by anyone's standards -- arms-control advocates warn that the high-energy-density physical realm it explores could still lead to advances.

Arjun Makhijani, president of the Institute for Energy and Environmental Research, told us, "To some extent, NIF and the others are pure research, but you know the nuclear folks cannot be kept happy with just experiments, they will be asked to produce, or the money will be cut off. ... If they don't do that, they will be laid off, so the question is how long a rope the military establishment will give them."

1. Energy deposited in outer shell; 2. Outer shell implodes; 3. Fuel is compressed; 4. Burn wave propagates through fuel; 5. Outer shell expands and fuel cools. Here's how a laser would trigger fusion. The implosion of the outer shell causes compression, fusion, and expansion. Sandia National Laboratories

Although NIF may have a nifty web site, the machine itself is in trouble, says Christopher Paine, a longtime observer of things nuclear, who works for the Natural Resources Defense Council. "The focusability, pulse duration, every parameter is now in question."

If too little energy hits the target, NIF may not initiate fusion -- its major goal. From the standpoint of fourth-generation nuclear weapons, however, that may be a good thing....

And while some people see NIF as a step toward fourth-generation nuclear weapons, others see it as a tool to lure scientists to weapons labs. Michael Levi, of the nuclear security program at the Federation of American Scientists, says, "The JASONS [an elite defense advisory group] and the [national] labs acknowledge that NIF is a recruitment tool. It may be a recruitment tool with some unfortunate side effects regarding diplomatic, international relations...".

This pinch is a cinch
For an alternative, and much cheaper way of compressing matter and starting fusion, what about the Z-pinch? The funky moniker comes from geometry, where the "Z" axis goes up and down.

A Z-pinch machine forces intense current through a fine, cylindrical wire mesh. The current vaporizes the wires, forming a plasma -- an ionized gas -- and creates a huge magnetic field that accelerates the plasma inward, toward the Z axis. When the plasma becomes unstable, it creates a brief, intense X-ray shower, which does the compressing.

The particle beam fusion accelerator, Z-pinch version at Sandia National Lab has already created a pulse of X-rays with 290-trillion watts of power, which was, very briefly, 50 times the total output of all electric-generators on Earth!

That's an intensity NIF may eventually provide, but Z-pinch is not only cheaper and simpler -- it also hit those numbers back in 1998.

Vertically oriented yellow blobs indicate X-raysFor an alternative, and much cheaper way of compressing matter and starting fusion, what about the Z-pinch? The funky moniker comes from geometry, where the "Z" axis goes up and down. Glow indicates intense X-rays created in the Z-pinch device. Sandia National Laboratories

We should stress that blasts of X-rays aren't just interesting physics: A shower of X-rays, delivered by the fission primary, compresses fusion fuel and starts a thermonuclear bomb.

That could explain why the Z-pinch is happening at Sandia, one of the three giant Department of Energy labs. But it may be simply a fusion-power experiment. Neal Singer, a Sandia spokesman, described the effort as "an experimental machine that could possibly -- if enlarged -- produce usable electrical power through nuclear fusion." As a trigger for a nuclear device, he says, it would be "very unworkable. We're talking a machine of several hundred tons."

Former nuclear-weapon designer Ray Kidder, however, admits to concern about technologies that could replace the heavy capacitors powering the pinch, particularly a Russian gadget that generated electricity with conventional explosives. "Some technology they were putting in was excellent," he says. "I consider their latest design ... ingenious."

Kidder, who says most fourth-generation nuclear weapons are speculative at best, suggests banning the combination of high-explosive current generators and fusion research. "That's where you better start watching out, because if it worked, it might actually prove to have lethality."

Pure fusion = Sure confusion?
In what is apparently the only non-classified treatment of fourth-generation nuclear weapons (see "Fourth Generation ..." in the bibliography), Swiss physicist Andre Gsponer listed other "blue sky" advanced weapons. While we mention them largely for theoretical interest, there has been some limited progress recently.

Giant submarine plows through the water. This here Trident-class nuclear sub carries quite a thermonuke wallop. Do we really need new, improved nukes? National Atomic Museum.

One obvious -- but technically thorny -- bomb would exploit the mutual annihilation of matter and antimatter, which supposedly releases the ultimate in energy per unit of mass. Although tiny quantities of antimatter have finally been produced at the CERN physics research facility in Europe, they are nowhere near enough to make a weapon. And nobody seems to have solved the problem of separating antimatter from regular matter (as soon as they meet, it's annihilations-ville). The antimatter lasted for only a few microseconds...

A second possible source of energy is nuclear isomers, isotopes with equal numbers of neutrons and protons that can exist in two energy states. Per unit of mass, nuclear isomers may be 1 percent as powerful as a fission reaction.

In 1999, a group lead by Carl Collins of the University of Texas at Dallas, and including a researcher from the Air Force Research Laboratory, made gamma rays with the nuclear isomer hafnium 178. Collins told Science magazine (see "First Light..." in the bibliography) that the isomer packed quite a wallop, indicating that it might have other capabilities beyond making the first gamma-ray laser: "You could set off something the size of a matchhead" and sterilize a wide area contaminated by biological weapons.

Can we make sense of the 4-gen problem?

 

 

 

 

 

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